Mobile waste water treatment device

ABSTRACT

A simple, rapid, efficient and inexpensive process for on-site recycling of wastewater with minimal odor wherein the solid wastes generated by the water treatment process are dewatering on-site by solar energy to water content levels. below those required for disposal. All operations, including solar dewatering, are accomplished in a compact unit which may be mobile. The solar dewatering unit includes a drying pan over which a solar collector window arrangement is disposed. 
     In the process, wastewater, a water purifying composition and an oxidizing agent are additively mixed together in a first reactor settling tank and the resulting composition is neutralized to a pH of between 7.5-9.4. The added water purifying composition is then allowed to precipitate wherein it binds to and precipitates heavy metals as well as other impurities. The precipitated purifying composition forms a non-hazardous sludge at the bottom of the tank. The resulting supernatant is pumped through a filter to yield recycled wastewater suitable for disposal or reuse. The remaining sludge is pumped to a third tank where it is accumulated and thickened. Once a sufficient amount of sludge is accumulated, the sludge is pumped to a solar dewatering unit where the sludge is dried to a water content level below 50% water which is suitable for landfill disposal.

This is a continuation of application Ser. No. 08/016,788, filed Feb.11, 1993, now U.S. Pat. No. 5,336,398.

FIELD OF THE INVENTION

The present invention relates to a wastewater treatment process. Morespecifically, the present invention relates to a recycling wastewatertreatment process useful for on-site removal of heavy metals, fats,oils, grease and paint residues from wastewater and the subsequenton-site treatment of the solid waste generated from the wastewatertreatment process.

BACKGROUND OF THE INVENTION

Most industries are presently faced with significant waste disposalproblems. As the world becomes more ecologically aware and asgovernments enact stricter environmental laws, the need for simple,efficient and effective methods for treating waste will increase.

Of particular concern in the area of industrial waste management is thetreatment of wastewater. An additional, related concern to the treatmentof wastewater is the subsequent treatment and disposal of the solidwastes generated from wastewater treatment processes.

I. Wastewater Treatment

On-site wastewater treatment processes are especially needed in light ofthe volume and mobility of this form of waste as well as the enactmentof stricter regulatory laws. For example, Congress recently enacted theClean Water Act (CWA-PL92-500), which established a framework for thedischarge of treated wastewater to the waters of the United States. Oneof the provisions of this law levies a $25,000 per day per wasteconstituent fine against violators. Provisions of the Clean Water Acthave also recently been expanded to cover both point and non-pointdischarges to the waters of the United States.

The provisions of the non-point regulations address the concerns ofmixing industrial wastewater with storm water runoff. Two industriesparticularly impacted by these recent enactments to the Clean Water Actare the transportation and construction industries. Transportationindustries must now control incidental losses of oil and grease fromvehicle operation. Construction industries must now control the contentand turbidity of their storm water runoff.

The marine cargo container maintenance industry has been significantlyimpacted by these changes to the Clean Water Act. The fact is that mostcompanies in this industry currently violate the Clean Water Act bytheir uncontrolled discharge of untreated water. Under current industrypractice, the untreated water generated from cleaning marine containersis presently allowed to drain to the ground after washing. Thiswastewater eventually mingles with storm water when rain occurs. Thisresults in a violation of the Clean Water Act whenever there israinwater runoff.

In order to enable better on-site wastewater management and to assistcompanies in complying with the Clean Water Act, a simple, efficient,and economical on-site device and process for treating and recyclingwastewater is needed.

Wastewater is heavy and therefore costly to transport to off-site watertreatment facilities. Further, given storage constraints, wastewatertreatment will generally be required frequently. Therefore, it isimportant that wastewater treatment systems be simple to operate so asto enable those relatively unskilled in the art of wastewater treatmentto practice the wastewater treatment process on-site. Simplicity ofoperation is also an important factor for keeping the cost of watertreatment to a minimum.

Water recycling systems also require that there be interim wastewaterstorage. In order to minimize the capital costs associated with theinterim storage facility, the water purification system must be capableof processing large amounts of water rapidly.

Another area of concern regarding wastewater treatment is theminimization of the total volume of wastewater generated. In some areas,water is scarce and/or expensive. In such areas, it is particularlydesireable to minimize the volume of water employed. In addition, thecost of wastewater disposal is increasing rapidly everywhere. Apurification system that recycles wastewater has the further advantageof minimizing the total volume of wastewater that is ultimatelygenerated. Volume minimization also serves to facilitate the containmentand isolation of the waste contaminants. Thus, a closed loop processcapable of recycling one batch of wastewater over and over again isparticularly desirable.

Numerous methods have been developed for the removal of wastes fromwastewater. For example, agents have been added to wastewater thatchemically react with the contaminants. Chemical processes often havethe disadvantages of being time consuming and requiring complex reactioninstallations resulting in considerable capital costs. In addition,chemical methods commonly cause the formation of gaseous wastes thatalso require proper disposal.

One area of particular concern regarding wastewater treatment is theremoval of heavy metals from wastewater. Heavy metals, such as copper,iron, silver, zinc, nickel, lead, cadmium and chromium pose severehealth and environmental dangers due to the high toxicity of thesemetals. Zeolites (Perman, U.S. Pat. No. 5,071,587) and anionicpolyelectrolytes (Monick, et al., U.S. Pat. No. 4,765,908) have beenused to remove heavy metals from wastewater solutions.

Water evaporation processes that yield a concentrated composition ofwaste contaminants have also been employed as a purification method.Water. evaporation has the disadvantage that it is energy intensive thusrendering this method of purification economically impractical. Inaddition, evaporation methodologies are not resource efficient wherewater is expensive and/or in short supply.

Fine suspended waste particles are commonly removed by chemicalflocculating agents capable of binding to these waste particles. Iron-IIsalts, aluminum sulfate, calcium hydrate compositions and lime or sodiumaluminate with activated silicic acid compositions are commonly employedas chemical flocculation agents. Chemical flocculating agents can bedeficient in the sense that they do not effectively remove solubilizedwaste components.

Additional water purification methods include those methods that causethermal, electrical and mechanical decomposition of the wastecontaminants.

II. Treatment and Disposal of Wastes Generated From Water TreatmentProcesses

A further concern regarding the treatment of wastewater is thesubsequent treatment and disposal of the solid wastes generated by watertreatment processes.

Currently, companies engaging in on-site wastewater treatment are forcedto transport the waste generated off-site for further dewatering inorder to comply with state standards. For example, in California, theWater Resources Control Board requires sludge to be dried to below a 50percent water content before it can be disposed of in a landfill.On-site mechanical dewatering, generally, cannot achieve this level ofdrying.

On-site mechanical dewatering is currently done by mechanically pressingor squeezing the water out of the sludge. Presently, this mechanicalprocess can only lower the water content to 60-70%. In addition, oncedried, the sludge must be stored in a dry environment in order toprevent the reabsorption of water until it can be transported forfurther processing. In light of the current need to ship partially driedsolids off-site for further dewatering, existing "on-site" wastewatertreatment facilities cannot be said to be completely "on-site."

In addition to being unable to yield a final disposable solid waste,current dewatering methods are labor intensive, cost inefficient andenvironmentally insensitive. In addition, substantial capital costs arerequired for both dewatering and storage.

The present need to transport wastes off-site for additional dewateringfurther increases already significant water treatment costs. The watercontent of the sludge needlessly escalates already high transportationcosts. Thus, an on-site means for achieving drier sludge, even if thatdrier sludge required further processing, would reduce the costs ofsolid waste disposal. Furthermore, it is environmentally wasteful totransport overly wet sludge. As energy costs increase, current methodsof solid waste disposal become increasingly impractical. Thus, asignificant need exists for an improved method for on-site dewatering ofsolid wastes.

SUMMARY OF THE INVENTION

In order to address these problems, the invention relates to anintegrated, mobile wastewater treatment device for the treatment ofheavy metals, paint residues, fats, oils and grease comprising areactor/settling tank in which wastewater is treated to yield asupernatant and a sludge, a filter through which the supernatant ispumped, a holding tank to which filtered supernatant is pumped, a secondholding tank to which sludge from the reactor/settling tank is pumped,and a solar dewatering unit for accumulating and thickening the sludge,wherein each of the tanks, filter and dewatering unit are configured sothat the entire system can be mounted on a chassis.

In a preferred embodiment, the wastewater treatment device furthercomprises a wash rack useful for collecting wastewater wherein thecollected wastewater is pumped to the reactor/settling tank fortreatment. The device is capable of automated operation.

In the most preferred embodiment, the tanks and filter are arrangedwithin a standard marine cargo container and the dewatering device ispositioned on the top of the container. The dewatering unit comprises adrying pan and a solar collector, such as a glass or plastic window,positioned over said pan.

The process of the instant invention comprises a first step whereinwastewater, a water purifying composition and an oxidizing agent areadditively mixed together in a first reactor/settling tank. During theadditive mixing, the pH of the resulting composition is neutralized to apH of between 7.5-9.4. In the second step of the process, the waterpurifying composition is allowed to precipitate wherein it binds to andprecipitates heavy metals as well as other impurities. The precipitatedpurifying composition forms a sludge at the bottom of the tank. In thethird step of the process, the resulting supernatant is pumped through afilter to yield recycled wastewater suitable for disposal or reuse. Theremaining sludge is pumped to a third tank where it is accumulated andthickened. Once a sufficient amount of sludge is accumulated, the sludgeis pumped to a solar dewatering unit where the sludge is dried to awater content level below 50% water which is suitable for landfilldisposal.

BRIEF DESCRIPTION OF THE FIGURES

The invention will be better understood by reference to the appendedFigures, of which:

FIG. 1 provides a schematic of an automated recycling water processaccording to the invention;

FIG. 2 provides a three-dimensional depiction of the automated recyclingwater process; and

FIG. 3 provides a detailed depiction of the solar dewatering unit of theinstant invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is a simple, rapid, efficient and inexpensiveprocess enabling the on-site continuous recycling of wastewater on alarge scale as well as the on-site treatment of the solid wastesgenerated by the water treatment process. The most preferred embodimentof the instant invention is shown in FIGS. 1-3 in which like numbers areused to designate the same elements in each figure. Thus, in thisembodiment, wastewater is accumulated in a several hundred gallonreactor/settling tank 1. The reactor/settling tank preferably possessesa cone shaped bottom which facilitates mixing and the subsequentformation and separation of the precipitated purifying composition atthe bottom of the tank. This tank design also enables enhancedsupernatant separation over other tank designs.

Once the wastewater to be treated has been placed in thereactor/settling tank, a water purifying composition and an oxidizingagent are additively mixed into the wastewater. The addition of thewater purifying composition and the oxidizing agent to the wastewater ispreferably done over a three minute period.

A wide variety of suitable purifying compositions are known in the artincluding those taught by Monick, et al. (U.S. Pat. No. 4,765,908),Piepho (U.S. Pat. No. 4,415,467), Piepho (U.S. Pat. No. 4,332,693) andHasegawa, et al. (U.S. Pat. No. 4,923,629).

The preferred purifying composition of the instant invention is AmericanColloid Company product number RM1080N4 (hereinafter "RM1080N4")(American Colloid Company 150 West Shure Drive, Arlington Heights,Ill.). RM-1080N4 is a bentonite clay composition that acts as a chemicalbinding agent. RM1080N4 acts by binding to the heavy metals, oils andgrease in the wastewater. Shortly after introducing RM1080N4 to thewastewater, RM1080N4 forms a sweep floc causing the heavy metal, oil andgrease impurities to settle at the bottom of the cone shapedreactor/settling tank. As a bentonite clay agent, RM1080N4 has theadvantage that it does not change the pH of the wastewater solution.Other water purification reactants commonly contain aluminum sulfate orlime which alter the pH of the wastewater. It is preferred that 5.1pounds of RM1080N4 per 100 gallons of wastewater is used.

An oxidizing agent is used to oxidize solids and inhibit the formationof foul smelling odors. Sodium hypochlorite is the preferred oxidant.Preferably, 1 pound of neat sodium hypochlorite is used per 1000 gallonsof wastewater. During the addition of the purifying composition and theoxidant, the resulting solution is preferably mixed at G≧100/second toensure adequate dispersion of purifying composition throughout thewastewater.

The pH of the treatment mixture is neutralized to pH 7.5-9.4 using astrong base. Soda ash is the preferred base. A pump 2 delivering thebase to the reactor/settling tank is automatically electronicallycoordinated with a pH meter and a neutralization controller 3 toregulate the pH of the treatment composition.

Once the purifying composition and oxidizing agent are introduced, theresulting mixture is allowed to stand until the purifying compositionforms a floc that settles to the bottom of the tank in the form of asludge. The resulting supernatant is clear.

Once the floc settles, the supernatant is pumped from thereactor/settling tank through a filter, preferably a 10 micron Bagfilter 4 and into a holding tank S from which the treated water can bepumped for reuse.

The supernatant is preferably pumped through a port 6 at the top of thecone-shaped portion of the reactor/settling tank. This method ofseparating the supernatant from the precipitated sludge is advantageousover separating the supernatant by draining the wastewater over aseparation device such as a belt filter as it reduces the amount offiltration and filtration equipment required. Simplified filtration ofthe supernatant enables greater trouble free operation and thus reducesoperational downtime and costs.

Once the supernatant has been removed from the reactor/settling tank,the sludge is pumped into a third tank 7 where the sludge is accumulatedand thickened.

Once a sufficient amount of sludge has been accumulated and thickened,the sludge is pumped to a solar dewatering unit 8 located on top of thewater treatment facility. The solar dewatering unit consists of adrainable drying pan 9 covered by a solar collecting device 10. Thisarrangement provides a utilized water treatment/recycling unit which canadvantageously be moved from site to site, for example to differentareas in a chemical plant. The unit can also be positioned at a marinecargo container terminal which will allow the proper disposal ofwastewater and solid residues from such sites. Since, as shown in FIG.2, the unit can be built into a standard cargo container (shown bydashed lines), the unit provides an integrated, mobile treatment systemwhich will solve the compliance problems of many smaller companies orprocessors who, at the present time, generate only relatively smallamounts of contaminated water and cannot justify the capital expenditureof an on-site treatment system.

The solar collecting device acts very much like a green house,collecting solar radiation in order to accelerate the drying process.Through the use of sunlight energy, the solar dewatering unit is able toreduce the water content of the sludge to below 50 percent, thepercentage water content currently required by many landfills for thedisposal of solid wastes. The primary purpose of the solar collectingdevice is to focus solar energy on to the sludge. The solar collectingdevice also serves to divert incidental rainfall. The solar collectingdevice generally consists of a translucent material such as a clearplastic. The solar collecting device should be at least partiallyremovable from the drying pan in order to allow access for removal ofthe sludge.

The drying pan possesses an underdrain system 11 that allows for thedrainage of water. The drying pan can be of varying size. The drying panis preferably mounted atop a water treatment container that issufficiently large to dry over six months of accumulated sludge at atime.

In order for the treatment process to be a recycling process, a washrack 12 capable of holding large volumes of water is arranged so thatthe wash rack receives and stores the wastewater effluent. The wash rackis also coordinated so that it supplies the reactor/settling tank withwastewater for treatment. Thus, the wash rack completes the closed loopenabling the same batch of water to be continuously used and recycled.

A typical water quality profile for industrial wastewater generated bymarine cargo container washout water is shown in Table 1.

                  TABLE 1                                                         ______________________________________                                                Untreated Water                                                                             Treated Water                                                                              Removal                                    Metal   Content (ppm) Content (ppm)                                                                              (%)                                        ______________________________________                                        Copper  0.11          0.06         55                                         Nickel  0.4           0.04         90                                         Zinc    14.0          1.42         90                                         Chromium                                                                              2.0           0.02         90                                         ______________________________________                                    

In a further embodiment of the present invention, the above describedpurification system is automated such that the addition of base toneutralize the pH, the addition of the oxidizing agent, the addition ofthe water purifying composition, the operation of the mixer, and thevarious pumps are electronically coordinated 13 for automated operation.This embodiment of the present invention facilitates the on-site use ofthe instant invention by those of relatively little skill in the art.

The above described purification system can be portable both within thetreatment site and from site to site. The system can be arranged in arelatively compact space such that it will fit on a standard truckchassis. As noted above, the solar dewatering unit is preferably placedon the roof of the treatment facility. Thus, given the compactarrangement of the purification system of the present invention, it ispossible to place the entire wastewater processing system on atransportation means such as a standard chassis. The transportability ofthe instant invention presents a significant advantage since mostcontainer maintenance depots are operated on leased land. Therefore itis desireable to be able to transport the purification system from siteto site.

The instant invention provides several advantages over the prior art.The instant invention provides a single step, operationally simpleprocess for the removal of impurities including heavy metal, fats, oils,grease and paint residues from wastewater. It has the further advantagethat it enables on-site dewatering of the generated solid wastes towater content levels below 50 percent. It is important to note that theinstant invention can be practiced through the combination of relativelyinexpensive, commercially available equipment and compositions. Thus, alarge capital investment for custom designed equipment is not requiredto practice the invention. The invention is also energy efficient, onlyrequiring energy input for pumping the wastewater and sludge and for themixing required during the addition of the purifying composition andoxidant. Significant energy costs for dewatering the resulting solidwastes are avoided since solar energy is employed. The water treatmentprocess of the invention is also operational on a larger scale, enablingthe processing of up to 16,000 gallons per day using a 350 gallonsettling tank. The process is also operationally simple, capable ofautomated operation which thus eliminates the need for skilledoperators.

It is understood that the above described purification system can bescaled up or down depending on the needs of the users. Furthermore, itis within the skill of one of ordinary skill in the art to arrange thetanks and filters in series in order to accommodate the purification ofgreater volumes per unit time.

What is claimed is:
 1. A mobile waste water treatment device having afirst portion for waste water treatment and a second portion fordewatering sludge generated by said treatment, said first portionarranged within a marine cargo container and said second portion mountedon the top of said container, said first portion for waste watertreatment comprising:a) a reactor-settling tank having a waste waterinlet port, a supernatant outlet port and a sludge outlet port; b) afirst holding tank; c) a second holding tank; d) means for pumpingsupernatant liquid from said supernatant outlet port through a filteringmeans to said first holding tank; e) means for pumping sludge from saidsludge outlet port to said second holding tank; f) means for pumpingsludge from said second holding tank to said second portion fordewatering sludge; andsaid second portion for dewatering sludgeincluding a solar dewatering unit comprising: a) a sludge dewateringpan; b) drain means forming a portion of said pan for permitting thedrainage of liquid from sludge in said pan to said second holding tank;c) a translucent solar collecting device positioned over said pan. 2.The waste water treatment device of claim 1 further comprising a washrack, the wash rack having a volume sufficient to receive and storewaste water effluent from said first holding tank.
 3. The waste watertreatment device of claim 1 further comprising means for adding pHneutralizing materials, oxidizing agents and water purifyingcompositions to said reactor-settling tank.